Die for molding honeycomb structure and manufacturing method thereof

ABSTRACT

A die for extrusion-forming a honeycomb structure which includes: a die base provided with ceramic puddle introducing holes and slits in communication with the ceramic puddle introducing holes; and a substrate layer, which roughly defines the final width of the slits, and a surface layer, which precisely defines the final width of the slits, formed on the die base in this order so that the final width of the slits becomes 15 to 200 μm, wherein the surface layer is made up of tungsten carbide particles which are 5 μm or less in average particle diameter and contain W 3 C as a main ingredient. According to this invention, there is provided a die for extrusion-forming a honeycomb structure which can restrain fluctuation in extrusion-forming speed among its parts and resistance to pushing force, both caused at the time of extrusion-forming, to be very small and is superior in productivity and durability.

TECHNICAL FIELD

This invention relates to a die used when a honeycomb structure isextrusion-formed and a manufacturing method thereof and, in moreparticular, a die for extrusion-forming a honeycomb structure whichincludes: a die base; and a substrate layer and a surface layer whichare formed on the die base so as to provide the die base with slits of aspecified width and a manufacturing method thereof.

BACKGROUND ART

Conventionally, ceramic honeycomb structures have been widely used as,for example, a filter for purifying exhaust gases and a catalystcarrier, etc. In recent years, as the regulation of exhaust gas has beentightened, there have been increasing demands for a honeycomb structure,as a filter, whose partition walls are as thin as 120 μm or less so thatit can achieve higher exhaust gas purifying performance. The partitionwalls of the honeycomb structure are expected to become thinner more andmore in the future.

As a method for manufacturing such honeycomb structures,extrusion-forming has been generally used, and it is the width of theslits provided on their dies that determine the thickness of thepartition walls of the honeycomb structures when manufacturing them byextrusion-forming. Thus, a variety of dies have been disclosed whoseslits width is adjusted by forming coating layers on their bases.

Specifically, there is disclosed a die, as one example of conventionaldies for forming honeycomb structures, whose slit width is adjusted byforming a coating layer on its base by electroless plating(JP-A-61-39167).

Further, there is disclosed another die for extrusion-forming ahoneycomb structure whose resistance to abrasion is improved by forming,by chemical vapor deposition (CVD), a coating layer consisting of ironboride, chromium carbide, aluminum oxide, titanium carbide, titaniumnitride, or titanium nitride carbide on it die base (JP-A-60-145804).

In the die for extrusion-forming a honeycomb structure described in theabove patent document 1, the abrasion resistance of the coating layer isnot necessarily sufficient to extrude ceramic materials, since thecoating layer is formed by electroless nickel plating.

In the die disclosed in JP-A-60-145804, since the thickness of thecoating layer formed by chemical vapor deposition (CVD) is up to about30 μm, it is very difficult to provide slits of 120 μm or less wide, solong as the coating layer is formed by chemical vapor deposition on thedie base where slits have been roughly provided by electrical dischargemachining or grinding. Thus, even with this die, a honeycomb structurethat complied with the recent demands could not be obtained.

In the meantime, there is disclosed in JP-A-2002-1716 a method formanufacturing a die for use in extrusion-forming of ceramic honeycombstructures which employs a die member provided with forming grooves andceramic puddle feeding holes and includes a step of depositing ahardwearing material at least on the surface of the forming grooves bychemical vapor deposition, wherein the forming grooves of the die memberare formed by grinding with a grinding stone, an electroless platinglayer is formed at least on the surface of the forming grooves, andtungsten carbide as a hardwearing material is deposited on theelectroless plating layer at 300° C. to 600° C.

Further, there is proposed in JP-A-10-309713 a die for use inextrusion-forming of a ceramic honeycomb structure whose base isprovided with slits 30 to 200 μm wide, wherein the slit width is firstroughly adjusted by forming a substrate layer on the base by electrolessplating and then adjusted to be 30 to 200 μm by forming a surface layerconsisting of W₂C by chemical vapor deposition (CVD).

In these conventional manufacturing methods, however, what is disclosedis just to make up the surface layer of tungsten carbide or of amaterial containing W₂C particles as a main ingredient, and they are notintended at all to make the surface layer or the hardwearing materialprovided on the die base a dense and uniform one.

Specifically, in the die obtained by the manufacturing method describedin JP-A-2002-1716, since it is not manufactured taking intoconsideration the composition and particle diameter of the tungstencarbide which constitutes the hardwearing material, the speed ofextrusion-forming ceramic puddle is apt to vary from part to part of thedie at the time of extrusion-forming, whereby its formability is notnecessarily satisfactory. Particularly when extrusion-forming ahoneycomb structure whose partition wall thickness is 70 μm or less,poor forming is apt to occur, which has been a serious problem inmeeting the demands for much thinner partition walls of honeycombstructures.

Further, in both the die obtained by the manufacturing method describedin JP-A-2002-1716 and the die described in JP-A-10-309713, since thehardwearing material or the surface layer is made up of a material thatcontains a relatively large amount of W₂C, their surface roughness islarge and their resistance to pushing force is relatively large at thetime of extrusion-forming. Thus, with these dies, the extrusion-formingspeed is low, and productivity of honeycomb structures leaves room forimprovement. Furthermore, there arises another problem, due to largefriction produced on the surface of the dies when ceramic puddle movingthrough their slits, of making the hardwearing material or the surfacelayer susceptible to abrasion.

DISCLOSURE OF THE INVENTION

This invention has been made in light of the above described problemswhich have been left unresolved by the prior art. And after focusing agreat deal of effort on examining the problems, the present inventorshave found that a surface layer which contains W₃C of very smallparticle diameter as a main ingredient and has a uniform and smallsurface roughness can be selectively formed by restricting theconditions under which the surface layer is formed by chemical vapordeposition within a specified range, in particular, by restricting theatmospheric temperature and pressure within a specified range. Thus, thepresent invention have been completed.

That is, according to the present invention there is provided a die forextrusion-forming a honeycomb structure (hereinafter sometimes referredto simply as “die”) which includes: a die base provided with ceramicpuddle feeding holes and slits in communication with the ceramic puddlefeeding holes; a substrate layer, which roughly defines the final widthof the slits, and a surface layer, which precisely defines the finalwidth of the slits, formed on the above die base in this order so thatthe final width of the slits becomes 15 to 200 μm, characterized in thatthe surface layer is made up of tungsten carbide particles which are 5μm or less in average particle diameter and contain W₃C as a mainingredient.

The term “main ingredient” herein used means an ingredient having thehighest content among the ingredients constituting the surface layer.

Preferably the die of this invention includes a substrate layer of 10 to100 μm thick and a surface layer of 1 to 30 μm thick formed on its basein this order. More preferably the surface layer of the die contains W₃Cparticles of 5 μm or less in average diameter and 5 μm or less inmaximum diameter as a main ingredient.

This invention can be preferably applied to a die whose slit width is 15to 70 μm.

In the meantime, this invention provides a method for manufacturing adie for extrusion-forming a honeycomb structure, as a method suitablyused for manufacturing the above described die, which includes the stepsof: forming a substrate layer, by the processes including electrolessplating, on the die base provided with ceramic puddle introducing holesand slits in communication with the ceramic puddle introducing holes;and forming a surface layer on the substrate layer by chemical vapordeposition (CVD) so as to provide slits of a specified width (e.g. of 10to 200 μm width), characterized in that the formation of the surfacelayer by chemical vapor deposition (CVD) is carried out while feeding areaction gas consisting of WF₆, C₆H₆ and H₂ to a reaction chamber at anatmospheric temperature of 310 to 420° C. and at an atmospheric pressureof 1 to 35 Torr.

The term “atmospheric pressures” herein used means pressure measured inthe vicinity of one end of the die base where the reaction gas flowsout.

Preferably a W/C molar ratio of the reaction gas in this invention is0.6 to 6.

Preferably the formation of the surface layer by chemical vapordeposition (CVD) in this invention is carried out while varying theatmospheric temperature and pressure in the reaction chamber dependingon the desired final width of the slits provided on the die.Specifically, when providing slits of 15 to 70 μm width, preferably theformation is carried out while feeding a reaction gas consisting of WF₆,C₆H₆ and H₂ to a reaction chamber at an atmospheric temperature of 310to 380° C. and at an atmospheric pressure of 1 to 30 Torr. Andparticularly preferably the formation of the surface layer by chemicalvapor deposition (CVD) is carried out at an atmospheric temperature of340 to 360° C.

As described above, in this invention, the width of the slits relativelyroughly formed on the die base is narrowed, by forming a substrate layeron the die base through the use of electroless plating that can providea coating layer with a wide range of thickness, to such an extent thatit can be adjusted to a desired final width by forming a surface layeron the substrate layer through the use of chemical vapor deposition(CVD).

This invention makes it possible to provide slits having width asextremely small as about 200 μm or less with a high accuracy bylaminating the surface layer through the use of chemical vapordeposition (CVD) that can control the thickness of a coating layer at alevel of 1 μm. Accordingly, with the die for extrusion-forming ahoneycomb structure of this invention, a honeycomb structure whosepartition walls are as thin as 200 μm or less, or as thin as 150 μm orless, or furthermore as thin as 70 μm or less can be manufactured with ahigh accuracy.

In addition, in the die of this invention, not only the problems ofvariation in extrusion-forming speed among the parts and increase inresistance to pushing force, which are usually caused at the time ofextrusion-forming when using a die having slits of extremely small widthas above, but also the problems of deterioration of abrasion resistanceon the surface and decrease in productivity of a honeycomb structure,which accompany the above described problems, are solved by making upits surface layer of a specified material.

Specifically, in the die of this invention, its surface is allowed to besmooth and of uniform in the roughness by making up its surface layer oftungsten carbide particles which are 5 μm or less in average particlediameter, more preferably 5 μm or less in average particle diameter and5 μm or less in maximum particle diameter, and contain W₃C as a mainingredient. Thus, in the die of this invention, the flow of ceramicpuddle is more smooth and uniform at every part, compared with theconventional dies, whereby extrusion-forming of a honeycomb structurecan be performed in state where resistance to pushing force is low andfluctuation in extrusion-forming speed among the parts hardly occurs.Thus, according to the die of this invention, a honeycomb structure canbe formed while completely avoiding poor forming, even when thepartition walls of the object honeycomb structure are as thin as 70 μmor less. Further, according to the die of this invention, theextrusion-forming speed can be easily improved since the die can extrudeceramic puddle at lower pressures, resulting in improvement inproductivity of a honeycomb structure. Still further, according to thedie of this invention, since the friction created on the surface of thedie and the pressure applied to the die when ceramic puddle movesthrough its slits are decreased, the durability of the surface layer isimproved and the restrictions placed on the die in terms of its strengthis reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a schematic cross-sectional view of a die forextrusion-forming a honeycomb structures in accordance with oneembodiment of this invention and

FIG. 1( b) is a partially enlarged view of FIG. 1( a); and

FIG. 2 is a partially enlarged view of a die substrate of this inventionschematically showing one example of slits and ceramic puddleintroducing holes provided in the die substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

The mode for carrying out this invention will now be described in detailwith reference to the drawings.

As shown in FIGS. 1( a), 1(b) and 2, a die 1 of this invention includes:a die base 11 provided with ceramic puddle introducing holes 4 and slits2 in communication with the ceramic puddle introducing holes 4; and asubstrate layer 12, which roughly defines the final width of the slits,and a surface layer 13, which precisely defines the final width of theslits, formed on the die base 11 in this order so that the final widthof the slit 2 becomes 15 to 200 μm, the die 1 being characterized inthat the surface layer 13 is made up of tungsten carbide particles whichare 5 μm or less in average particle diameter and contain W₃C as a mainingredient.

In the die 1 thus constructed, both the fluctuation in extrusion-formingspeed among its parts and resistance to pushing force, which are causedat the time of extrusion-forming, are extremely small and itsproductivity and durability are superior. In the following the die 1will be described in detail in terms of its constituents.

As shown in FIG. 2, a die base 11 of this invention is usually providedwith ceramic puddle introducing holes 4 formed on the surface 7 on theopposite side B to the formed product extruding side and provided withslits 2 formed, for example, in a grid arrangement on the surface 6 onthe formed product extruding side A so that they communicate with theceramic puddle introducing holes 4.

The ceramic puddle introducing holes 4 are usually provided so that theycorrespond to the positions where slits 2 intersect each other, and theceramic puddle obtained by kneading ceramic raw materials etc. isintroduced into the die 1 through the ceramic puddle introducing holes4, and the formed product of a honeycomb structure is extruded throughthe slits 2.

As shown in FIG. 1, the die 1 of this invention includes a substratelayer 12, which roughly defines the final width of the slits, on itsbase 11.

The substrate layer 12 of this invention is formed with the objectmainly of narrowing the width of the slits 2 having been roughly formedby machining etc. to such an extent that the slits can have a desiredfinal width if a surface layer is provided on the substrate layer 12 bychemical vapor deposition (CVD) described later, and the thickness ofthe substrate layer 12 can be suitably selected from this viewpoint.

The substrate layer 12 may consist of a single layer or more than onelayer. Accordingly, the thickness of the substrate layer 12 can also becontrolled using the number of layers constituting the substrate layer.

However, the substrate layer 12 is usually provided to have thickness inthe range of 10 to 100 μm, preferably in the range of 10 to 60 μm.

In the substrate layer 12 of this invention, its material is notparticularly limited; however, preferably it is made up of a materialwhich contains at least one selected from the group consisting ofnickel, cobalt and copper, as a main ingredient, and particularlypreferably which contains nickel as a main ingredient, because thesubstrate layer made up of such a material has a high joining strengthto a surface layer, which is provided on the substrate layer andcontains W₃C as a main ingredient as described later.

The die 1 of this invention further includes a surface layer 13, whichprecisely defines the final width of the slits, on the substrate layer12 described above, and the surface layer 13 is provided whilecontrolling its thickness precisely at a level of 1 μm so that thethickness is in the range of 1 to 30 μm.

In this invention, such a surface layer is made up of tungsten carbideparticles which are 5 μm or less in average particle diameter andcontain W₃C as a main ingredient.

However, the tungsten carbide particles constituting the surface layerof this invention may contain at least one selected from the groupconsisting of W₂C, WC and W as an ingredient other than W₃C. Further,the tungsten carbide particles may be crystalline, noncrystalline, ormixed crystalline particles.

Preferably the surface layer 13 of this invention contains as a mainingredient W₃C particles 3.0 μm or less in average particle diameter,more preferably W₃C particles 2.0 μm or less in average particlediameter, much more preferably W₃C particles 0.5 μm or less in averageparticle diameter, much more preferably W₃C particles 0.4 μm or less inaverage particle diameter, and particularly preferably W₃C particles 0.1μm or less in average particle diameter.

Making up the surface layer 13 mainly of W₃C particles with such anaverage particle diameter permits the resistance to pushing force at thetime of extrusion-forming to be decreased and the durability andproductivity of the die to be improved.

Preferably the surface layer 13 of this invention contains as a mainingredient W₃C particles 6.0 μm or less in maximum particle diameter,more preferably W₃C particles 5.0 μm or less in maximum particlediameter, much more preferably W₃C particles 1.0 μm or less in maximumparticle diameter, and particularly preferably W₃C particles 0.5 μm orless in maximum particle diameter.

If one uses W₃C particles having the maximum particle diameter in such arange as a main ingredient, the fluctuation in extrusion-forming speedamong the parts of the die may lessen further.

The surface layer 13 of this invention may consist of a single layer ormore than one layer. Accordingly, the thickness of the surface layer 13can be controlled using the number of layers constituting the surfacelayer; however, from the viewpoint of simplification of themanufacturing process, preferably the surface layer 13 consists of asingle layer.

No restrictions other than those having been described so far arenecessarily imposed on the die of this invention; however, in order toimprove the strength of a honeycomb structure with thin partition walls,which is likely to be low due to the thin partition walls, preferablythe corner portions 5 formed on the intersections of the slits 2 of thedie 1 is rounded to be of R shape. The R shape is not particularlylimited as long as it has a natural radius; however, preferably the Rshape has a 15 to 80 μm radius of curvature.

Next, a method for manufacturing the die of this invention will bedescribed.

In the method of this invention, first, ceramic puddle introducing holesand slits which communicate with the ceramic puddle introducing holesare made on a die base by machining such as ECM, EDM or grinding. Inthis step, the width W of the slits may be specified to be a littlewider than a desired final width and in the precision range which can beaccomplished by ECM, EDM or grinding. However, taking into considerationthe layer thickness which electroless plating and chemical vapordeposition (CVD) can accomplish, preferably the width W is in the rangeof 150 to 300 μm. A specified number of slits can be provided in adesired arrangement, such as a grid arrangement, and in specifiedintervals, depending on the shape of the object honeycomb structure.Preferably the ceramic puddle introducing holes which communicate withthe slits are made so that they open on the face of the die baseopposite to the face in which the slits have been cut and are in thepositions corresponding to the intersections of the slits.

Then, in the method of this invention, a substrate layer is formed onthe above described die base by a process including electroless plating.

Preferably, the substrate layer of this invention is provided so thatthe slit width is narrowed to an extent that it can have a desired finalwidth if a surface layer is formed on the substrate layer by chemicalvapor deposition (CVD) described later. Usually the thickness of thesubstrate layer provided is 10 to 100 μm, preferably 10 to 60 μm, sinceit is also necessary to take into consideration the thickness which canbe formed by a process including electroless plating. Forming thesubstrate layer by a process including electroless plating permits thecorner portions of the die formed on the intersections of the slits tobe of R shape having a natural radius.

Preferably the process including electroless plating of this inventionis carried out while avoiding the formation of oxide layers as amixture.

Specifically, the process including electroless plating carried out inthis invention is (1) a process of forming a substrate layer at onecontinuous electroless plating, (2) a process of forming a substratelayer in an inert gas atmosphere by electroless plating, (3) a processof forming a substrate layer while measuring, in an electroless platingsolution, the slit width obtained by forming the substrate layer on thedie base, (4) a process of forming a substrate layer by electrolessplating and then forming another substrate layer by electroplating onthe formed substrate layer, or (5) a process of forming a substratelayer by electroless plating and then pickling the surface of the formedsubstrate layer with dilute nitric acid, acetic acid, etc. Each of theseprocesses can be carried out alone or two or more can be carried out incombination.

When forming the substrate layer by the process (1), in order to easilycontrol the thickness of the substrate layer, it is preferable to firstprepare a plurality of dummies on which slits of the same width as thoseof the die base are formed and immerse them in the plating bath and thencarry out the process while monitoring the slit width of the dummies.

When forming the substrate layer by the process (5), in order to ensurethat oxide layers are not formed in the substrate layer, it ispreferable to carry out the pickling operation in an inert gasatmosphere.

Preferably the substrate layer of this invention is made up of amaterial which contains at least one selected from the group consistingof nickel, cobalt and copper, as a main ingredient, and particularlypreferably which contains nickel as a main ingredient, because thesubstrate layer made up of such a material has a high joining strengthto a surface layer described later. Electroless plating can be carriedout by conventional procedure. For example, it can be carried out byheating a plating solution containing the above metal and a reductantsuch as sodium hypochlorite or sodium borohydroxide to about 80 to 100°C. and immersing the die base in the plating solution for a specifiedtime.

The corner portions of the intersections of the slits are allowed to beof R shape that has an arbitrary radius of curvature by changing theconcentration of the electrolytic solution, the materials for plating,etc. when forming the substrate layer by electroless plating.

After forming the above described substrate layer, a surface layer isformed by chemical vapor deposition (CVD), which can precisely controlthe thickness of a layer to be formed and make the same uniform, so asto provide slits of 200 μm or less wide.

The reaction gas for use in chemical vapor deposition of this inventionconsists of WF₆, C₆H₆ and H₂. To form a surface layer which contains W₃Cat a high rate, preferably the W/C molar ratio is set for 0.6 to 6, morepreferably 0.6 to 5, and particularly preferably 0.6 to 3.

In this invention, when carrying out chemical vapor deposition (CVD),the above reaction gas is introduced into a reaction chamber whoseatmospheric temperature is set for 310 to 420° C. and atmosphericpressure for 1 to 35 Torr.

When the atmospheric temperature is higher than 420° C., even if theabove reaction gas is used, a surface layer is formed which contains notonly W₃C particles, but also W₂C particles of large particle diameter ata high rate and non-uniformly. As a result, the surface of the obtaineddie is rough and its surface roughness is non-uniform from part to part,which causes wide fluctuation in extrusion-forming speed among the partsof the die and high resistance to pushing force at the time ofextrusion-forming. On the other hand, when the atmospheric temperatureis lower than 310° C., a surface layer is formed which contains Wparticles at a high rate, which results in unsatisfactory adhesion tothe substrate layer. Thus, the surface layer is likely to peel off atthe time of extrusion-forming, causing deterioration of the die'sdurability.

When the atmospheric pressure in the reaction chamber is higher than 35Torr, the partial pressure of the reaction gas is increased and thereactivity is also increased, leading to formation of a surface layerwhich contains not only W₃C particles, but also W₂C particles of largeparticle diameter at a high rate and non-uniformly. As a result, thesurface of the obtained die is rough and its surface roughness isnon-uniform from part to part.

In this invention, preferably the above atmospheric temperature andpressure are selected depending on the final width of the die slitsaimed at.

Specifically, when producing a die for extrusion-forming a honeycombstructure, the narrower the final width of the die slits becomes, thelower the flow rate of the reaction gas passing on the surface of thedie base becomes; in such a situation, the reaction of the reaction gashaving the above described concentration becomes easy to accelerate. Andthe formation of W₂C particles is accelerated, a surface layer is easyto form which contains not only W₃C particles, but also W₂C particles ata high rate, which results in a surface layer having a non-uniform andhigh surface roughness. On the other hand, the wider the final width ofthe die slits becomes, the higher the flow rate of the reaction gaspassing on the surface of the die base becomes; in such a situation, thereaction gas having the above described concentration becomes lessreactive. And the film formation rate is lowered, causing decrease inproductivity, while the formation of W particles is accelerated,resulting in decrease in adhesion to the substrate layer.

Accordingly, in this invention, in order to form a surface layer whichcontains W₃C particles at a high rate, has a uniform and low surfaceroughness, and good adhesion to the substrate layer, it is preferable toselect conditions under which the reaction gas is less reactive, thatis, select an atmosphere of lower temperature or pressure as the finalwidth of the die slits is decreased, whereas it is preferable to selectconditions under which the reaction gas is more reactive, that is,select an atmosphere of higher temperature or pressure as the finalwidth of the die slits is increased.

In more particular, for example, when the final slit width is set formore than 70 μm and 200 μm or less, preferably the atmospherictemperature of the reaction chamber is 320 to 400° C., more preferably340 to 370° C., and particularly preferably 340 to 360° C.

Similarly, when the final slit width is set for more than 70 μm and 200μm or less, the atmospheric pressure of the reaction chamber can be 1 to35 Torr, preferably 1 to 30 Torr.

For example, when the final slit width is set for 15 to 70 μm,preferably the atmospheric temperature of the reaction chamber is 310 to380° C., more preferably 330 to 370° C., and particularly preferably 340to 360° C.

Similarly, when the final slit width is set for 15 to 70 μm, theatmospheric pressure of the reaction chamber is preferably 1 to 30 Torr,more preferably 1 to 20 Torr, still more preferably 1 to 15 Torr, andparticularly preferably 1 to 10 Torr.

In the die of this invention, the total thickness of the substrate layerand the surface layer is not particularly limited, and suitablethickness can be appropriately selected depending on the width of theslits formed by machining such as EDM or grinding at the beginning.

However, to permit the above described corner portions of the die to beof R shape having a radius suitable for improving the strength of thehoneycomb structure to be produced, and to use as few processes aspossible for forming coating layers having desired properties so thatproduction costs are reduced, preferably the total thickness of thesubstrate layer and the surface layer is 20 to 70 μm. The R shape can bemaintained by providing a surface layer of uniform thickness on asubstrate layer by chemical vapor deposition (CVD).

In the following this invention will be described in detail in terms ofits practical examples; however, it should be understood that theseexamples are not intended to limit this invention.

EXAMPLE 1

First, a plate material consisting of SUS was machined on a lathe and agrinding wheel to be a square plate 250 mm×250 mm×20 mm(length×breadth×thickness). Then, slits 180 μm wide and 3.0 mm deep werecut at 1.0 mm intervals in one end face of the square plate by EDM andgrinding. And another slits were cut in the same manner as above so thatthey were at right angles to the above cut slits. In the meantime,ceramic puddle introducing holes 1.00 mm in diameter and 18 mm deep weremade at 1.0 mm intervals in the other end face of the square plate byECM in such a manner as to position their central axes at theintersections (every other intersection) of the above cut slits so thatthey were in communication with the slits.

Then, the square plate thus obtained was machined into a disk 200 mm inoutside diameter by EDM, degreased, and immersed in a 35% hydrochloricacid bath for one minute to be pre-treated. After that, the disk wasplated in a nickel phosphate bath at one continuous electroless platingoperation so as to form a substrate layer 40 μm thick on its surface. Inthe mean time, a plurality of dummies consisting of the same material asthe die base were prepared and subjected to plating by electrolessplating in the same manner as above. In the course of the platingoperation, the dummies were taken out one by one with the lapse of timeso as to monitor the thickness of their substrate layers.

Then, the disk with a substrate layer formed on its surface was allowedto stand still in a reaction chamber at an atmospheric temperature of350° C. and an atmospheric pressure of 10 Torr, subjected to chemicalvapor deposition (CVD) while feeding a reaction gas consisting of WF₆,C₆H₆ and H₂ (W/C molar ratio: 0.8) to the reaction chamber to form asurface layer 15 μm thick, and fitted in a given frame to give a die.

The die for extrusion-forming a honeycomb structure thus obtained wassuch that its slit width W was about 70 μm (180−(40+15)×2) and thecorner portions formed on the intersections of its slits in a gridarrangement were of R shape with a radius of curvature of about 35 μm.

EXAMPLE 2 AND COMPARATIVE EXAMPLES 1, 2

Dies for use in forming of honeycomb structures were obtained in thesame manner as in example 1 except that the disks with a substrate layerformed on their surfaces were allowed to stand still in reactionchambers at atmospheric temperatures of 330° C., 400° C. and 300° C. andan atmospheric pressure of 10 Torr, respectively, so that they weresubjected to chemical vapor deposition (CVD).

The dies for use in extrusion-forming of honeycomb structures thusobtained were such that the width W of their slits was about 70 μm andthe corner portions formed on the intersections of their slits in a gridarrangement were of R shape with a radius of curvature of about 35 μm.

(Evaluation)

In the die of example 1 having been subjected to chemical vapordeposition (CVD) at an atmospheric temperature of 350° C., its surfacewas uniformly lustrous. And the observation under an electron microscoperevealed that the surface was made up of particles 0.5 μm or less indiameter and 0.1 μm in average diameter and had a uniform surfaceroughness. When analyzing the material of its surface layer using X-raydiffraction, the spectra obtained were mostly those of W₃C. And whenusing the die in extrusion-forming of the ceramic puddle containing acordierite raw material as a main ingredient, a honeycomb structure withpartition walls of 70 μm thick was obtained without causing poorforming.

In contrast with this, in the die of example 2 having been subjected tochemical vapor deposition (CVD) at an atmospheric temperature of 330°C., its surface was less lustrous than that of example 1. And theobservation under an electron microscope revealed that the whole surfacewas made up of particles 1.0 μm or less in diameter and 0.5 μm inaverage diameter and the particles of each diameter had a littlenon-uniform distribution. When analyzing the material of its surfacelayer using X-ray diffraction, though the spectra obtained were mostlythose of W₃C, there were mixed peaks of W component spectra at a highrate compared with that of the die of example 1. And when using the diein extrusion-forming of the ceramic puddle containing a cordierite rawmaterial as a main ingredient, though a honeycomb structure withpartition walls of 70 μm thick was obtained without causing poorforming, the resistance pressure at the time of extrusion-forming wasincreased compared with that of the die of example 1.

In the die of comparative example 1 having been subjected to chemicalvapor deposition (CVD) at an atmospheric temperature of 400° C., itssurface was lusterless. And the observation under an electron microscoperevealed that the whole surface was made up of particles 2 to 6 μm indiameter (3 μm in average diameter) and the particles of each diameterhad a non-uniform distribution. When analyzing the material of itssurface layer using X-ray diffraction, the spectra obtained were mostlythose of W₂C. And when using the die in extrusion-forming of the ceramicpuddle containing a cordierite raw material as a main ingredient so asto produce a honeycomb structure, the extrusion-forming speed variedwidely from part to part of the die, as a result, no honeycomb structurewas produced. The resistance pressure at the time of extrusion-formingwas increased compared with that of the die of example 2.

In the die of comparative example 2 having been subjected to chemicalvapor deposition (CVD) at an atmospheric temperature of 300° C., itssurface was considerably poor in luster. And the observation of thesurface and the cross section of the die under an electron microscoperevealed that the surface was made up of particles 3 μm or less indiameter and 2 μm in average diameter and part of the surface layerpeeled off the substrate layer. When analyzing the material of itssurface layer using X-ray diffraction, the spectra obtained were mostlythose of W. And when using the die in extrusion-forming of the ceramicpuddle containing a cordierite raw material as a main ingredient so asto produce a honeycomb structure, the surface layer of the die peeledoff in a short period of time. The results are summarized in Table 1.

TABLE 1 Material Surface Average Maximum Atmospheric of RoughnessParticle Particle Temperature Surface of Die Resistance Peeling DiameterDiameter (° C.) layer Surface Pressure Formability Properties (μm) (μm)Comparative 400 W₂C mixed high, non- large poor not 3.0 6.0 Example 1 ata high uniform peeled rate Example 1 350 W₃C low, small satisfactory not0.1 0.5 present uniform peeled at a high rate Example 2 330 W mixed alittle a little satisfactory not 0.5 1.0 at a low high, a large peeledrate little non- uniform Comparative 300 W mixed a little — — peeled 2.03.0 Example 2 at a high high, non- rate uniform *Table 1 shows theresults obtained when setting the atmospheric pressure for 10 Torr andthe final slit width for 70 μm.

EXAMPLE 3

First, a plate material consisting of SUS was machined on a lathe and agrinding wheel to be a square plate 250 mm×250 mm×20 mm(length×breadth×thickness). Then, slits 180 μm wide and 3.0 mm deep werecut at 1.5 mm intervals in one end face of the square plate by EDM andgrinding. And another slits were cut in the same manner as above so thatthey were at right angles to the above cut slits. In the meantime,ceramic puddle introducing holes 1.40 mm in diameter and 18 mm deep weremade at 1.5 mm intervals in the other end face of the square plate byECM in such a manner as to position their central axes at theintersections (every other intersection) of the above cut slits so thatthey were in communication with the slits.

Then, the square plate thus obtained was machined into a disk 200 mm inoutside diameter by EDM, degreased, and immersed in a 35% hydrochloricacid bath for one minute to be pre-treated. After that, the disk wasplated in a nickel phosphate bath at one continuous plating operation byelectroless plating so as to form a substrate layer 25 μm thick on itssurface. In the mean time, a plurality of dummies consisting of the samematerial as the die base were prepared and subjected to plating byelectroless plating in the same manner as above. In the course of theplating operation, the dummies were taken out one by one with the lapseof time so as to monitor the thickness of their substrate layers.

Then, the disk with a substrate layer formed on its surface was allowedto stand still in a reaction chamber at an atmospheric temperature of350° C. and an atmospheric pressure of 10 Torr, subjected to chemicalvapor deposition (CVD) while feeding a reaction gas consisting of WF₆,C₆H₆ and H₂ (W/C molar ratio: 0.8) to the reaction chamber to form asurface layer 15 μm thick, and fitted in a given frame to give a die.

The die for extrusion-forming a honeycomb structure thus obtained wassuch that its average slit width W was 100 μm (180−(25+15)×2) and thecorner portions formed on the intersections of its slits in a gridarrangement were of R shape with a radius of curvature of about 25 μm.

EXAMPLES 4, 5 AND COMPARATIVE EXAMPLES 3, 4

Dies for use in extrusion-forming of honeycomb structures were obtainedin the same manner as in example 3 except that the disks with asubstrate layer formed on their surfaces were allowed to stand still inreaction chambers at atmospheric temperatures of 400° C., 330° C., 300°C. and 450° C. and an atmospheric pressure of 10 Torr, respectively, sothat they were subjected to chemical vapor deposition (CVD) to form asurface layer 15 μm thick on the substrate layer.

The dies thus obtained were such that the width of their slits was about100 μm and the corner portions formed on the intersections of theirslits in a grid arrangement were of R shape with a radius of curvatureof about 25 μm.

(Evaluation)

The results obtained from examples 3, 4 and comparative examples 3, 4had basically the same tendency as those of examples 1, 2 andcomparative examples 1, 2 where the final slit width was set for 70 μm;however, in the die of examples 3, 4 and comparative examples 3.4, itwas observed that the suitable atmospheric temperature range of chemicalvapor deposition (CVD) was shifted toward the higher temperature rangebecause their final slit width was set for 100 μm. In the following theevaluation results will be described for each example and comparativeexample.

In the die of example 3 having been subjected to chemical vapordeposition (CVD) at an atmospheric temperature of 350° C., its surfacewas uniformly lustrous. And the observation under an electron microscoperevealed that the surface was made up of particles 0.5 μm or less indiameter and 0.1 μm in average diameter and had a uniform surfaceroughness. When analyzing the material of its surface layer using X-raydiffraction, the spectra obtained were mostly those of W₃C.

When using the die in extrusion-forming of the ceramic puddle containinga cordierite raw material as a main ingredient and drying and firing theobtained formed product, a honeycomb structure with partition walls of100 μm thick was obtained without causing poor forming.

In contrast with this, in the die of example 4 having been subjected tochemical vapor deposition (CVD) at an atmospheric temperature of 400°C., its surface was less lustrous than that of example 3. And theobservation under an electron microscope revealed that the whole surfacewas made up of particles 5 μm or less in diameter and 2 μm in averagediameter and the particles of each diameter had a little non-uniformdistribution. When analyzing the material of its surface layer usingX-ray diffraction, though the spectra obtained were mostly those of W₃C,there were mixed spectra of W₂C at a high rate compared with that of thedie of example 3.

When using the die in extrusion-forming of the ceramic puddle containinga cordierite raw material as a main ingredient and drying and firing theobtained formed product, though a honeycomb structure with partitionwalls of about 100 μm thick was obtained without causing poor forming,the resistance pressure at the time of extrusion-forming was a littleincreased compared with that of the die of example 3.

In the die of comparative example 3 having been subjected to chemicalvapor deposition (CVD) at an atmospheric temperature of 450° C., itssurface was lusterless. And the observation under an electron microscoperevealed that the whole surface was made up of particles 3 to 10 μm indiameter (4 μm in average diameter) and the particles of each diameterhad a non-uniform distribution. Further the thickness of the surfacelayer at the portions where slits were cut was non-uniform from theinside of the slits to the openings of the same and the difference inthickness observed was as large as 20 times. When analyzing the materialof its surface layer using X-ray diffraction, the spectra obtained weremostly those of W₂C. And when using the die in extrusion-forming of theceramic puddle containing a cordierite raw material as a main ingredientso as to produce a honeycomb structure, the extrusion-forming speedvaried widely from part to part of the die, as a result, no honeycombstructure was produced. And the resistance pressure at the time ofextrusion-forming was increased compared with that of the die of example4.

In the die of example 5 having been subjected to chemical vapordeposition (CVD) at an atmospheric temperature of 330° C., its surfacewas a little less lustrous compared with example 3. And the observationof the surface under an electron microscope revealed that the wholesurface was made up of particles 1 μm or less in diameter and 0.5 μm inaverage diameter and the particles of each particle diameter had alittle non-uniform distribution. When analyzing the material of itssurface layer using X-ray diffraction, though the spectra obtained weremostly those of W₃C, there were mixed peaks of W component spectra at ahigh rate compared with that of the die of example 3. And when using thedie in extrusion-forming of the ceramic puddle containing a cordieriteraw material as a main ingredient, though a honeycomb structure withpartition walls of 100 μm thick was obtained without causing poorforming, the resistance pressure at the time of extrusion-forming was alittle increased compared with that of the die of example 3.

In the die of comparative example 4 having been subjected to chemicalvapor deposition (CVD) at an atmospheric temperature of 300° C., itssurface was a considerably poor in luster. And the observation of thesurface and the cross section of the die under an electron microscoperevealed that the surface was made up of particles 3 μm or less indiameter and 2 μm in average diameter and part of the surface layerpeeled of f the substrate layer. When analyzing the material of itssurface layer using X-ray diffraction, the spectra obtained were mostlythose of W. And when using the die in extrusion-forming of the ceramicpuddle containing a cordierite raw material as a main ingredient so asto produce a honeycomb structure, the surface layer of the die peeledoff in a short period of time. The results are summarized in Table 2.

TABLE 2 Material Surface Average Maximum Atmospheric of RoughnessParticle Particle Temperature Surface of Die Resistance Peeling DiameterDiameter (° C.) layer Surface Pressure Formability Properties (μm) (μm)Comparative 450 W₂C mixed high, large poor not 4.0 10 Example 3 at ahigh non- peeled rate uniform Example 4 400 W₂C mixed a little a littlea little not 2.0 5.0 at a high, a large poor peeled somewhat little highnon- rate uniform Example 3 350 W₃C low, small satisfactory not 0.1 0.5present uniform peeled at a high rate Example 5 330 W mixed a little alittle satisfactory not 0.5 1.0 at a low high, a large peeled ratelittle non- uniform Comparative 300 W mixed a little — — peeled 2.0 3.0Example 4 at a high high, rate uniform (thickness is non- uniform)*Table 2 shows the results obtained when setting the atmosphericpressure for 10 Torr and the final slit width for 100 μm.

COMPARATIVE EXAMPLE 5, EXAMPLE 6

Dies were obtained in the same manner as in example 1 except that thedisks with a substrate layer formed on their surfaces were allowed tostand still in reaction chambers at atmospheric pressures of 50 Torr and30 Torr and an atmospheric temperature of 350° C., respectively, so thatthey were subjected to chemical vapor deposition (CVD).

The dies thus obtained were such that the width of their slits was about70 μm and the corner portions formed on the intersections of their slitsin a grid arrangement were of R shape with a radius of curvature ofabout 35 μm.

(Evaluation)

In the die of example 6 having been subjected to chemical vapordeposition (CVD) at an atmospheric pressure of 30 Torr, its surface waspartially less lustrous than that of example 1. And the observationunder an electron microscope revealed that the whole surface was made upof particles 5 μm or less in diameter and 2 μm in average diameter andparticles of large diameter (about 5 μm in diameter) were locallyunevenly distributed. When analyzing the material of its surface layerusing X-ray diffraction, though the spectra obtained were mostly thoseof W₃C, there were mixed spectra of W₂C at a high rate compared withthat of the die of example 1. When using the die in extrusion-forming ofthe ceramic puddle containing a cordierite raw material as a mainingredient, though a honeycomb structure with partition walls of 70 μmthick was obtained without causing poor forming, the resistance pressureat the time of extrusion-forming was a little increased compared withthat of the die of example 1.

In the die of comparative example 5 having been subjected to chemicalvapor deposition (CVD) at an atmospheric pressure of 50 Torr, therelocally occurred lusterless portions on its surface. And the observationunder an electron microscope revealed that the surface was made up ofparticles 2 to 10 μm in diameter (4 μm in average diameter) andparticles of large diameter (about 10 μm in diameter) were locallyunevenly distributed on the lusterless portions. When analyzing thematerial of its surface layer using X-ray diffraction, it was found thatW₂C particles were mixed at a high rate at the lusterless portions. Whenusing the die in extrusion-forming of the ceramic puddle containing acordierite raw material as a main ingredient, the extrusion-formingspeed varied widely from part to part of the die, as a result, nohoneycomb structure was produced. And the resistance pressure at thetime of extrusion-forming was increased compared with that of the die ofexample 6. The results are summarized in Table 3.

TABLE 3 Surface Average Maximum Atmospheric Material Roughness ParticleParticle Pressure of Surface of Die Resistance Diameter Diameter (Torr)layer Surface Pressure Formability (μm) (μm) Comparative 50 W₂C locallyhigh, large poor 4 10 Example 5 mixed at a non- (locally high rateuniform unevenly distributed) Example 6, 30 W₂C locally a little alittle a little 2 5 mixed at a high, a large poor (locally) low ratelittle unevenly non- distributed) uniform Example 1 10 W₂C present low,small satisfactory   0.1 0.5 at a high uniform rate *Table 3 shows theresults obtained when setting the atmospheric temperature for 350° C.and the final slit width for 70 μm.

COMPARATIVE EXAMPLE 6, EXAMPLE 7

Dies were obtained in the same manner as in example 3 except that thedisks with a substrate layer formed on their surfaces were allowed tostand still in reaction chambers at atmospheric pressures of 50 Torr and30 Torr and an atmospheric temperature of 350° C., respectively, so thatthey were subjected to chemical vapor deposition (CVD).

The dies for use in forming of honeycomb structures thus obtained weresuch that the width of their slits was about 100 μm and the cornerportions formed on the intersections of their slits in a gridarrangement were of R shape with a radius of curvature of about 25 μm.

(Evaluation)

The results obtained from comparative example 6 and example 7 hadbasically the same tendency as those of examples 1, 6 and comparativeexample 5 where the final slit width was set for 70 μm; however, in thedie of comparative example 6 and example 7, it was observed that thesuitable atmospheric pressure range of chemical vapor deposition (CVD)was shifted toward the higher pressure range because their final slitwidth was set for 100 μm. In the following the evaluation results willbe described for each example and comparative example.

In the die of example 7 having been subjected to chemical vapordeposition (CVD) at an atmospheric pressure of 30 Torr, the satisfactoryresults almost the same as those of example 3 were obtained.

In contrast with this, in the die of comparative example 6 having beensubjected to chemical vapor deposition (CVD) at an atmospheric pressureof 50 Torr, there locally occurred lusterless portions on its surface.And the observation under an electron microscope revealed that thesurface was made up of particles 2 to 8 μm in diameter (3 μm in averagediameter) and particles of large diameter (about 10 μm in diameter) werelocally unevenly distributed on the lusterless portions. When analyzingthe material of its surface layer using X-ray diffraction, it was foundthat W₂C particles were mixed at a high rate at the lusterless portions.When using the die in extrusion-forming of the ceramic puddle containinga cordierite raw material as a main ingredient, the extrusion-formingspeed varied widely from part to part of the die, as a result, nohoneycomb structure was produced. And the resistance pressure at thetime of extrusion-forming was increased compared with that of the die ofexample 7. The results are summarized in Table 4.

TABLE 4 Surface Average Maximum Atmospheric Material Roughness ParticleParticle Pressure of Surface of Die Resistance Diameter Diameter (Torr)layer Surface Pressure Formability (μm) (μm) Comparative 50 W₂C locallyhigh, large Poor 3.0 8.0 Example 6 mixed at a non- (locally high rateuniform unevenly distributed) Example 7 30 W₃C present low, smallSatisfactory 0.4 1.0 at a high uniform rate Example 3 10 W₃C presentlow, small Satisfactory 0.1 0.5 at a high uniform rate *Table 4 showsthe results obtained when setting the atmospheric temperature for 350°C. and the final slit width for 100 μm.

INDUSTRIAL APPLICATION

As described so far, according to this invention, are provided a die forextrusion-forming a honeycomb structure which can restrain fluctuationin extrusion-forming speed among its parts and resistance to pushingforce, both caused at the time of extrusion-forming, to be very smalland is superior in abrasion resistance of its surface, and therefore, issuitable for forming of honeycomb structures with partition walls asthin as 70 μm or less and a manufacturing method thereof.

1. A method for manufacturing a die for extrusion-forming a honeycombstructure, which comprises: forming a substrate layer, by a processincluding electroless plating, on a die base provided with ceramicpuddle introducing holes and slits in communication with the ceramicpuddle introducing holes; pickling surface of the formed substrate layerwith dilute acid; and forming a surface layer on the substrate layer bychemical vapor deposition (CVD) so as to provide slits of a specifiedwidth, wherein the formation of the surface layer by chemical vapordeposition (CVD) is carried out while feeding a reaction gas consistingof WF₆, C₆H₆ and H₂ to a reaction chamber at an atmospheric temperatureof 310 to 380° C. and at an atmospheric pressure of 1 to 35 Torr, thesurface layer is made of tungsten carbide particles which are 5 μm orless in average particle diameter and contain W₃C as a main ingredient,and the W/C molar ratio of the reaction gas is 0.6 to
 3. 2. The methodfor manufacturing a die for extrusion-forming a honeycomb structureaccording to claim 1, wherein the formation of the surface layer bychemical vapor deposition (CVD) is carried out while feeding a reactiongas consisting of WF₆, C₆H₆ and H₂ to a reaction chamber at anatmospheric pressure of 1 to 30 Torr so as to provide the slits withwidth 15 to 70 μm.
 3. The method for manufacturing a die forextrusion-forming a honeycomb structure according to claim 1, whereinthe formation of the surface layer by chemical vapor deposition (CVD) iscarried out at an atmospheric temperature of 340 to 360° C.
 4. Themethod for manufacturing a die for extrusion-forming a honeycombstructure according to claim 2, wherein the formation of the surfacelayer by chemical vapor deposition (CVD) is carried out at anatmospheric temperature of 340 to 360° C.
 5. The method formanufacturing a die for extrusion-forming a honeycomb structureaccording to claim 1, wherein the substrate layer of 10 to 100 μm thickand the surface layer of 1 to 30 μm thick are formed on the die base inthis order.
 6. The method for manufacturing a die for extrusion-forminga honeycomb structure according to claim 1, wherein the surface layercontains W₃C particles with average particle diameter of 5 μm or lessand maximum particle diameter of 5 m or less as a main ingredient. 7.The method for manufacturing a die for extrusion-forming a honeycombstructure according to claim 5, wherein the surface layer contains W₃Cparticles with average particle diameter of 5 μm or less and maximumparticle diameter of 5 μm or less as a main ingredient.
 8. The methodfor manufacturing a die for extrusion-forming a honeycomb structureaccording to claim 5, wherein the width of the slits is 15 to 70 μm. 9.The method for manufacturing a die for extrusion-forming a honeycombstructure according to claim 1, wherein the acid includes any of nitricacid and acetic acid.
 10. The method for manufacturing a die forextrusion-forming a honeycomb structure according to claim 1, whereinthe surface layer is made of tungsten carbide particles which are 3 μmor less in average particle diameter.
 11. The method for manufacturing adie for extrusion-forming a honeycomb structure according to claim 1,wherein the formation of the surface layer by chemical vapor deposition(CVD) is carried out at an atmospheric temperature of 350° C.
 12. Themethod for manufacturing a die for extrusion-forming a honeycombstructure according to claim 1, wherein the formation of the surfacelayer by chemical vapor deposition (CVD) is carried out at anatmospheric pressure of 10 to 20 Torr.
 13. The method for manufacturinga die for extrusion-forming a honeycomb structure according to claim 1,wherein the surface layer consists essentially of w₃c.
 14. A method formanufacturing a die for extrusion-forming a honeycomb structure, whichcomprises: forming a substrate layer, by a process including electrolessplating, on a die base provided with ceramic puddle introducing holesand slits in communication with the ceramic puddle introducing holes;pickling surface of the formed substrate layer with dilute acid; andforming a surface layer on the substrate layer by chemical vapordeposition (CVD) so as to provide slits of a specified width, whereinthe formation of the surface layer by chemical vapor deposition (CVD) iscarried out while feeding a reaction gas consisting of WF₆, C₆H₆ and H₂to a reaction chamber at an atmospheric temperature of 310 to 380° C.and at an atmospheric pressure of 1 to 35 Torr, a W/C molar ratio of thereaction gas is 0.6 to 3, and the surface layer being formed of W₃Cparticles, and showing a uniform roughness.
 15. The method formanufacturing a die for extrusion-forming a honeycomb structureaccording to claim 14, wherein the acid includes an of nitric acid andacetic acid.
 16. The method for manufacturing a die forextrusion-forming a honeycomb structure according to claim 14, whereinthe surface layer being formed of W₃C particles which are 3 μm or lessin average particle diameter.
 17. The method for manufacturing a die forextrusion-forming a honeycomb structure according to claim 14, whereinthe formation of the surface layer by chemical vapor deposition (CVD) iscarried out at an atmospheric temperature of 350° C.
 18. The method formanufacturing a die for extrusion-forming a honeycomb structureaccording to claim 14, wherein the formation of the surface layer bychemical vapor deposition (CVD) is carried out at an atmosphericpressure of 10 to 20 Torr.
 19. The method for manufacturing a die forextrusion-forming a honeycomb structure according to claim 14, whereinthe surface layer consists essentially of W₃C.